Even on the ground, space elevators may have uses
Balloon-borne platforms developed as precursors to space elevators could be used as high-altitude relay stations for wireless communications, a 60-day field test suggests.
The hope is that one day a space elevator, comprised of a robot that will climb a strong tether about 100,000 kilometres (60,000 miles) long, will be able to send humans or other cargo cheaply into space.
Balloon-borne platforms could act as high-altitude Wi-Fi stations (Image: LiftPort Group)
If the platforms were used as Wi-Fi stations, robots would one day be needed to climb up the tethers to deliver new helium tanks for the balloons (Image: LiftPort Group)
Developing the technology necessary to accomplish this goal will take years, but some progress has been made so far. LiftPort Group, based in Bremerton, Washington, US, stretched a cable 1.6 kilometres (1 mile) into the air in Arizona, US, in January 2006 using a cluster of three balloons (see Space-elevator tether climbs a mile high).
But that test lasted for only 6 hours. Now, LiftPort has finished a 60-day test with a 100-metre-long tether held aloft by four helium balloons. The test was designed to see what kinds of problems would crop up if such a platform were used to transmit Wi-Fi signals. The lofty platforms would be especially useful for providing Wi-Fi coverage to rural areas, says company president Michael Laine.
Swallows and bats
Overall, he says, the test went well, but there were several unexpected encounters with wildlife. More than a dozen insect colonies had been laid eggs on the tether, and in the first few days of the test, curious bats flew around the balloons, apparently attracted by the sound made by the tether's vibrations. Late in the test, swallows were also seen swooping down on the balloons, possibly to sip the morning dew on their surfaces.
"That's the difference between a 6-hour and a 60-day test," Laine told New Scientist.
The company also tested their climbing robot on this tether, even though it was not crucial to finding out whether the balloons would work as a Wi-Fi station. The robot will be necessary in the future for delivering new helium tanks to balloons at higher altitudes.
The team learned that if the tether is pulled hard by wind, it starts to buckle and deform slightly, creating crinkles. The robot climber hit these crinkles and could not proceed because they made the tether too thick for it to handle.
"We broke our robot by doing this," Laine says. "It's the kind of failure we never would have learned had we only been doing 6-hour tests." Future designs will have to incorporate sensors to tell the robot when it is about to encounter varying thicknesses.
Strong but thin
LiftPort is now working with North Carolina State University and Rutgers University, both in the US, to develop a 5-kilometre (3-mile) tether system. Several weeks ago, the company also made its own carbon nanotubes for the first time. Because carbon nanotubes are extremely thin but incredibly strong, they have been studied for use in a lightweight tether that could reach all the way to space.
Other groups are also working towards building a space elevator. On 20 and 21 October, more than 20 teams will compete in the second round of NASA's Beam Power and Tether Centennial Challenges, competitions to spur the development of technology required for a space elevator.
In the Beam Power challenge, teams will try to use light to power a robot that needs to climb 50 metres at a rate of 1 metre per second or faster. The Tether challenge will test the strength of the competitors' tethers. LiftPort will not compete in the contests, as Laine sits on the board of the California-based Spaceward Foundation, which partnered with NASA to put on the two challenges.
No one won the first competitions, which were held in October 2005.
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Even on the ground, space elevators may have uses - space - 26 September 2006 - New Scientist Space
